Boron ion implantation using alternative fluorinated boron precursors, and formation of large boron hydrides for implantation

ABSTRACT

Methods of implanting boron-containing ions using fluorinated boron-containing dopant species that are more readily cleaved than boron trifluoride. A method of manufacturing a semiconductor device including implanting boron-containing ions using fluorinated boron-containing dopant species that are more readily cleaved than boron trifluoride. Also disclosed are a system for supplying a boron hydride precursor, and methods of forming a boron hydride precursor and methods for supplying a boron hydride precursor. In one implementation of the invention, the boron hydride precursors are generated for cluster boron implantation, for manufacturing semiconductor products such as integrated circuitry.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is filed under the provisions of 35 USC §371 based onInternational Application No. PCT/US06/33899 filed Aug. 30, 2006, whichin turn claims priority of U.S. Provisional Patent Application No.60/712,647 filed Aug. 30, 2005. The disclosures of such internationalapplication and U.S. priority application are hereby incorporated hereinby reference in their respective entireties, for all purposes.

FIELD OF THE INVENTION

The present invention relates to improved methods of implanting boron,particularly to methods of implanting boron-containing ions usingboron-containing dopant species that are more readily cleaved than borontrifluoride, and compositions for use in same. The invention alsorelates to a process for supplying a boron hydride precursor, to amethod of forming a boron hydride precursor and to a source of boronhydride precursor.

DESCRIPTION OF THE RELATED ART

Ion implantation is used in integrated circuit fabrication to accuratelyintroduce controlled amounts of dopant impurities (e.g., boron) intomicroelectronic device wafers and is a crucial process inmicroelectronic/semiconductor manufacturing. In such implantationsystems, an ion source ionizes a desired dopant element gas (“thefeedstock”) and the ions are extracted from the source in the form of anion beam of desired energy. Extraction is achieved by applying a highvoltage across suitably shaped extraction electrodes, which incorporateapertures for passage of the extracted beam. The ion beam is thendirected at the surface of the workpiece, such as a microelectronicdevice wafer, in order to implant the workpiece with the dopant impurityand form a region of desired conductivity. Then, the implanted dopantatoms are activated by annealing to form an electrically active dopedregion.

Presently, there are upwards of 10-15 implantation steps in thefabrication of state of the art devices. Increasing wafer sizes,decreasing critical dimensions, and growing circuit complexity areplacing greater demands on ion implant tools, with respect to betterprocess control, the deliverance of high beam currents at low energies,and a decrease in the mean time between failures (MTBF).

Boron trifluoride (BF₃) has traditionally been the source of borondopant impurities. However, BF₃ is problematic in that it requires asignificant amount of energy to break the B-F bonds (757 kJ mole⁻¹)compared to other dopant species commonly used in ion implantation(e.g., As—H=274 kJ mole⁻¹ and P—H=297 kJ mole⁻¹). As a result, ionsources must run at high arc voltages when implanting boron. High arcvoltages create high energy ions that bombard the hot filament orcathode in the ion source region, contributing to sputter erosion andfailure of the cathode.

It was previously reported that nominally 80% of the BF₃ dopant suppliedto an ion implanter was vented intact, suggesting that either the BF₃was not ionized or, if so, the fragments recombined. Clearly, the lowionization of BF₃ at high arc voltages exacerbates an already highlyinefficient process.

Thus, there is a continuing need for providing alternativeboron-containing dopant precursors for use as the boron element gas soas to increase the MTBF, the process efficiency and the life of the tooland to decrease the buildup of nonvolatile species at the ion sourceregion.

Boron cluster implantation is a method for increasing ion implantefficiency at an energy level lower than that required for implantutilizing boron trifluoride. Typical methods of boron clusterimplantation use decaborane (B10) and octadecaborane (B18) boron hydrideprecursors. These precursors are solid at room temperature and haverelatively low vapor pressures. Use of these precursors involvessublimation of the precursor material from a remote container andtransfer of the resulting vapor along fluid flow lines to asemiconductor tool for cluster implantation. These processes involve thepotential adverse side effects of insufficient material flow andcondensation. In order to combat the former, the vessels containing thesolid sources must be heated to constant and precise temperatures. Inorder to prevent unwanted condensation, the lines leading to the toolneed to be heat traced.

Boron cluster implantation utilizing decaborane and octadecaborane asprecursors presents additional challenges, including those identifiedbelow:

-   -   heat tracing the solid container and transfer lines is costly,        cumbersome, difficult to implement in an ion implanter,        difficult to retrofit and prone to failure;    -   unbalanced heat loads can lead to condensation on cold spots        that can result in clogging or uneven flow rates;    -   excess heat applied to the solid materials can lead to        decomposition resulting in impurities and uneven flow rates;    -   the flow rate of sublimed materials depends on the available        surface area on the vaporizer. Over time, as a solid is depleted        and recrystallized, the surface area of the vaporizer decreases,        leading to a drop in flow rate over the lifetime of the charged        vaporizer;    -   metering the amount of material in the tool is very difficult        and is based solely on vapor pressure;    -   controlling delivery of the material to the tool is difficult        and costly;    -   the decaborane and octadecaborane materials are expensive; and    -   installation of the vaporizer adjacent to the ion source, often        done to minimize the issues with installing heat traced transfer        lines inside the implanter, is a dangerous practice that can        result in safety and code concerns.

Accordingly, there is a need in the art for new systems, methods andprecursors for cluster boron implantation, including a need for improvedmethods of delivery of precursors for cluster boron implantation to atool for implantation, which enable easy transport of the precursor tothe tool and increased boron ion implantation, as compared totraditional implantation of boron-containing ions.

SUMMARY OF THE INVENTION

The present invention relates to a method of implanting boron-containingions using boron-containing dopant species that are more readily cleavedthan boron trifluoride. More specifically, the present invention relatesto improving the efficiency, the MTBF and the life of the ion sourcehardware using boron-containing dopant species that are more readilycleaved than boron trifluoride.

In one aspect, the present invention relates to method of implantingboron-containing ions comprising:

-   -   ionizing vaporized boron-containing dopant species in a vacuum        chamber under ionization conditions to generate boron-containing        ions; and    -   accelerating the boron-containing ions by electric field to        implant boron-containing ions into a device substrate,    -   wherein the boron-containing dopant species consists essentially        of species other than BF₃.

According to another embodiment, the boron-containing dopant speciescontain less than 20 wt % BF₃, based on the total weight of theboron-containing dopant species, preferably less than 10 wt %, morepreferably less than 5 wt %, even more preferably the boron-containingdopant species are substantially free of BF₃. Most preferably theboron-containing dopant species are devoid of boron trifluoride.

In another aspect, the present invention relates to a method ofimplanting boron-containing ions comprising:

-   -   ionizing vaporized fluorinated boron dopant species in a vacuum        chamber under ionization conditions to generate boron-containing        ions; and    -   accelerating the boron-containing ions by electric field to        implant boron-containing ions into a device substrate,    -   wherein the fluorinated boron dopant species comprise a compound        selected from the group consisting of B₂F₄, B(BF₂)₃CO, BF₂CH₃,        BF₂CF₃, BF₂Cl, BFCl₂, BF(CH₃)₂, NOBF₄, NH₄BF₄, H₂BF₇, H₂B₂F₆,        H₄B₄F₁₀, H₂BFO₂, H₂B₂F₂O₃, H₂B₂F₂O₆, H₂B₂F₄O₂, H₃BF₂O₂, H₄BF₃O₂,        H₄BF₃O₃, B₈F₁₂, B₁₀F₁₂, and (F₂B)₃BCO.

Another aspect of the invention relates to compositions or reagentscomprising a boron-containing dopant species, wherein said compositionsor reagents are useful for boron-containing ion implantation. Accordingto one embodiment, the compositions or reagents consist essentially ofspecies other than BF₃. According to another embodiment, theboron-containing dopant species contain less than 20 wt % BF₃, based onthe total weight of the boron-containing dopant species, preferably lessthan 10 wt %, more preferably less than 5 wt %, even more preferably theboron-containing dopant species are substantially free of BF₃. Mostpreferably the boron-containing dopant species are devoid of borontrifluoride. According to another embodiment, the compositions orreagents comprise boron-containing dopant species that are readilycleaved at energies less than 700 kJ/mol, preferably less than 650kJ/mol, even more preferably less than 600 kJ/mol. According to onepreferred embodiment, the fluorinated boron dopant species comprises aboron-containing compound selected from the group consisting of B₂F₄,B(BF₂)₃CO, BF₂CH₃, BF₂CF₃, BF₂Cl, BFCl₂, BF(CH₃)₂, NOBF₄, NH₄BF₄, H₂BF₇,H₂B₂F₆, H₄B₄F₁₀, H₂BFO₂, H₂B₂F₂O₃, H₂B₂F₂O₆, H₂B₂F₄O₂, H₂B₂F₄O₂,H₄BF₃O₃, B₈F₁₂, B₁₀F₁₂, and (F₂B)₃BCO.

A still further aspect of the invention relates to storage and deliveryvessels suitable for use in delivery of a material to an ion implantsource, wherein the vessel comprises boron-containing dopant speciesaccording to the invention. According to one embodiment, the vessel is acylinder. According to another embodiment, the vessel is asubatmospheric vessel such as those described in U.S. Pat. Nos.5,518,528; 5,704,965; 5,704,967; 5,935,305; 6,406,519; 6,204,180;5,837,027; 6,743,278; 6,089,027; 6,101,816; 6,343,476; 6,660,063;6,592,653; 6,132,492; 5,851,270; 5,916,245; 5,761,910; 6,083,298;6,592,653; and U.S. Pat. No. 5,707,424, which are hereby incorporatedherein by reference, in their respective entireties. Preferred vesselsinclude, but are not limited to, SDS® and VAC® delivery vessels(available from ATMI, Inc., Danbury, CT, USA). According to anotherembodiment, the vessel is an ampoule such as those described in U.S. PatNos. 6,868,869; 6,740,586; U.S. Patent Application Ser. No. 10/201,518,issued Jul. 26, 2005 as U.S, Pat. No. 6,921,062; U.S. Patent ApplicationSer. No. 10/858,509, issued Nov. 27, 2007 as U.S. Pat. No. 7,300,038;U.S. Patent Application Ser. No. 10/625,179, issued Jun. 21, 2005 asU.S. Pat. No. 6,909,839; U.S. Patent Application Ser. No. 10/028,743,issued Oct. 12, 2004 as U.S. Pat. No. 6,802,294; U.S. Provisional PatentApplication Ser. No. 60/662,515; and U.S. Provisional Patent ApplicationSer. No. 60/662,396, which are hereby incorporated herein by reference,in their respective entireties.

In yet another aspect, the present invention relates to a method ofmanufacturing a microelectronic device, said method comprising ionizingvaporized fluorinated boron dopant species in a vacuum chamber underionization conditions to generate boron-containing ions, andaccelerating the boron-containing ions by electric field to implantboron-containing ions into a device substrate and optionally, assemblingsaid microelectronic device with said device substrate, wherein thefluorinated boron dopant species consists essentially of species otherthan BF₃. More preferably, the boron-containing dopant species aresubstantially free of BF₃, and most preferably the boron-containingdopant species are devoid of boron trifluoride.

Yet another aspect of the invention relates to improved microelectronicdevices, and products incorporating same, made using the methods andcompositions described herein, and optionally, incorporating themicroelectronic device into a product.

The invention also relates to a method of forming a boron hydrideprecursor and a method for supplying a boron hydride precursor. Morespecifically, the invention relates to boron hydride precursorsgenerated from boron-containing gas for cluster boron implantation.Additionally the invention relates to a source of boron hydrideprecursor.

In one aspect the invention provides a method of forming a boron hydrideprecursor for cluster boron implantation. The method comprises providinga boron-containing gas and inducing conversion of the boron-containinggas to higher order boron-containing clusters.

In another aspect the invention provides a method of supplying a boronhydride precursor for cluster boron implantation. The method comprisesproviding a boron-containing gas, inducing conversion of theboron-containing gas to higher order boron-containing clusters andsupplying the higher order boron-containing clusters to a tool forcluster boron implantation. In one embodiment, the conversion is carriedout in a reactor adjacent to the tool. In another embodiment, thereactor is within the tool.

In an additional aspect, the invention relates to a boron hydrideprecursor source, comprising:

-   -   a boron-containing gas source;    -   a reactor adapted for inducing conversion of boron-containing        gas from said boron-containing gas source, to higher order        boron-containing clusters;    -   flow circuitry interconnecting the boron-containing gas source        and the reactor; and    -   optionally a mass or pressure controller in said flow circuitry.

In another aspect, the invention relates to a microelectronic devicemanufacturing facility, comprising a boron hydride precursor source ofthe invention, and a microelectronic device manufacturing tool, coupledin flow communication with the boron hydride precursor source.

A further aspect of the invention relates to a method of manufacturing amicroelectronic device, comprising cluster boron ion implantation with acluster boron species formed by the method described above.

Yet another aspect of the invention relates to a method of cluster boronion implantation comprising use of a cluster boron species formed by themethod described above.

Other aspects, features and embodiments of the invention will be morefully apparent from the ensuing disclosure and appended claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a boron hydride precursordelivery system according to one embodiment of the invention.

FIG. 2 is a schematic representation of an in-line diborane concentratorsuch as may be usefully employed in the practice of the invention.

FIG. 3 is a schematic representation of a high pressure reactor, inwhich the high pressure is created by a constriction in the exit path,such that the boron cluster formation reaction within the reactor occursat a higher pressure than the pressure within the tool.

FIG. 4 is a schematic representation of a heated packed reactor such asmay be usefully employed in the practice of the invention.

FIG. 5 is a schematic representation of a reactor with a concentric tubedesign such as may be usefully employed in the practice of theinvention.

FIG. 6 is a schematic representation of a cold/hot reactor adapted foruse in a system of the invention.

FIG. 7 is a schematic representation of a multiple temperature heatedreactor for use in a system of the invention.

FIG. 8 is a schematic representation of a reactor that utilizes plasmaor electrical discharge and is adapted for use in a system of theinvention.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS THEREOF

The present invention relates to producing ion beams rich inboron-containing ions using alternative boron-containing precursors thatare more readily cleaved than boron trifluoride to improve theefficiency, MTBF and the life of the ion implanter.

The present invention also relates to methods of forming a boron hydrideprecursor for cluster ion implantation and a method for supplying such aprecursor for use in cluster ion implantation. Additionally, theinvention relates to a source for boron hydride precursors.

One embodiment of the invention relates to a method of implantingboron-containing ions using boron-containing dopant species that arereadily cleaved at energies less than 700 kJ/mol, preferably less than650 kJ/mol, even more preferably less than 600 kJ/mol. The inventionalso relates to compositions or delivery systems containing suchspecies.

As used herein, “ion source region” includes the vacuum chamber, thesource arc chamber, the source insulators, the extraction electrodes,the suppression electrodes, the high voltage insulators and the sourcebushing.

As used herein, “microelectronic device” corresponds to semiconductorsubstrates, flat panel displays, and microelectromechanical systems(MEMS), manufactured for use in microelectronic, integrated circuit, orcomputer chip applications and packaging. It is to be understood thatthe term “microelectronic device” is not meant to be limiting in any wayand includes any substrate that will eventually become a microelectronicdevice or microelectronic assembly.

As used herein, “precursor” includes any molecule or structure thatprecedes and is the source of another molecule or structure. As such a“boron precursor” is a precursor that contains boron and can be utilizedas a source for boron ions in various implantation methods. Similarly, a“boron hydride precursor” is a precursor that contains a boron hydrideand can be a source for boron ions in implantation.

Boron ions (B⁺) are typically implanted to form a p-type region in asilicon substrate however, also contemplated herein is a method ofmanufacturing a microelectronic device having a shallow p-type dopedregion, by implanting molecular ions containing boron, as is well knownto those skilled in the art. For example, a molecular ion such as BF₂ ⁺may be implanted in order to attain low effective boron energy at higherextracted energy of the BF₂ ⁺ ion.

It has been postulated by the present inventors that lowering the bondenergy of the boron-containing dopant compound will result in aconcomitant lowering of the required arc voltage, thus increasing thelife of the ion source.

Accordingly, one embodiment of the invention relates to a method ofimplanting boron-containing ions comprising ionizing a boron-containingdopant species at a high ionization efficiency of at least 15% using anarc voltage less than 100 volts, preferably less than 90 volts, morepreferably less than 80 volts, and most preferably less than 70 volts,using a conventional hot cathode ion source or comparable voltages usinganother ion source. Towards that end, in one aspect, the presentinvention relates to a method of implanting boron-containing ions into amicroelectronic device substrate, said method comprising vaporizingboron-containing precursor feedstock to generate vaporizedboron-containing dopant species (when the boron-containing precursorfeedstock is a liquid or solid), ionizing the vaporized boron-containingdopant species to generate boron-containing ions, and accelerating theboron-containing ions by electric field to implant same into themicroelectronic device substrate, wherein the boron-containing precursorfeedstock is devoid of substantial quantities of boron trifluoride.Preferably, the boron-containing precursor comprises a halogen speciesincluding fluorine, chlorine, bromine and iodine. More preferably, theboron-containing precursor is a fluorinated boron precursor. It is to beunderstood that reference to a fluorinated boron precursor hereinafteris not meant to be limiting in any way.

Boron-containing precursors contemplated herein include, but are notlimited to, B₂F₄, B(BF₂)₃CO, BF₂CH₃, BF₂CF₃, BF₂Cl, BFCl₂, BF(CH₃)₂,NOBF₄, NH₄, NH₄BF₄, H₂BF₇, H₂B₂F₆, H₄B₄F₁₀, H₂BFO₂, H₂B₂F₂O₃, H₂B₂F₂O₆,H₂B₂F₂, O₆, H₂B₂F₄O₂, H₃BF₂O₂, H₄BF₃O₃, B₈F₁₂, B₁₀F₁₂, (F₂B)₃BCO, andcombinations thereof. Alternatively, the fluorine atoms of theaforementioned boron-containing precursors may be partially or totallysubstituted with other halogen atoms (e.g., BCl₃, BBr₃, B₂Cl₄, etc.). Ina particularly preferred embodiment, the boron-containing precursorsinclude B₂F₄, which is expected to undergo homolytic cleavage at the B—Bbond at arc voltages that are lower than that needed to cleave the B—Fbond in BF₃. Accordingly, another embodiment of the invention relates toa method of implanting boron-containing ions comprising cleaving theboron-containing precursor at the B—B bond. Another embodiment of theinvention relates to compositions or delivery systems comprisingboron-containing precursors having at least one B—B bond

Preferably, the alternative boron-containing precursor species require adissociate energy in a range from about 100 kJ mole⁻¹ to about 650 kJmole⁻¹, more preferably 300 kJ mole⁻¹ to about 550 kJ mole⁻¹.

In another embodiment, the present invention relates to a method ofimplanting boron-containing ions into a microelectronic devicesubstrate, said method comprising vaporizing boron-containing precursorfeedstock to generate vaporized boron-containing dopant species (whenthe boron-containing precursor feedstock is a liquid or solid), ionizingthe vaporized boron-containing dopant species to generateboron-containing ions, and accelerating the boron-containing ions byelectric field to implant same into the microelectronic devicesubstrate, wherein the boron-containing precursor feedstock comprisesboron trifluoride and at least one additional boron-containing precursorselected from the group consisting of B₂F₄, B(BF₂)₃CO, BF₂CH₃, BF₂CF₃,BF₂Cl, BFCl₂, BF(CH₃)₂, NOBF₄, NH₄BF₄, H₂BF₇, H₂B₂F₆, H₄B₄F₁₀, H₂BFO₂,H₂B₂F₂O₃, H₂B₂F₂O₆, H₂B₂F₄O₂, H₃BF₂O₂, H₄BF₃O₂, H₄BF₃O₃, B₈F₁₂, B₁₀F₁₂,(F₂B)₃BCO, and combinations thereof. Alternatively, the fluorine atomsof the aforementioned boron-containing precursors may be partially ortotally substituted with other halogen atoms (e.g., BCl₃, BBr₃, B₂Cl₄,etc.).

In another embodiment, the alternative boron-containing precursorspecies include higher order boranes and carboranes, smallnido-carboranes such as CB₅H₉, C₂B₄H₈, C₃B₃H₇, C₄B₂H₆, and C₂B₃H₇; opencage carboranes such as C₂B₃H₇, CB₅H₉, C₂B₄H₈, C₃B₃H₇, C₄B₂H₆, C₂B₇H₁₃;the small closo-carboranes such as C₂B₃H₅, C₂B₄H₆, C₂B₅H₇, CH₅H₇,C₂B₆H₈, C₂B₇H₉, C₂B₈H₁₀, C₂B₉H₁₁, C₂B₁₀H₁₂. In addition, derivatives ofthese carboranes may be used to modify and optimize the chemicalproperties of the carboranes (i.e vapor pressure, toxicity, reactivity)in combination with a fluorine source. Higher order boranes andcarboranes tend to be more stable compounds than the halogenatedboron-containing precursors and may provide B_(x)H_(y) fragments atlower arc voltages for ion implantation. Optionally and preferably, whenthe boron-containing precursor species include the higher order boranesand/or carboranes, the boron-containing precursor feedstock includes atleast one alternative fluorine source (e.g., F₂).

In yet another embodiment, the alternative boron-containing precursormay include at least one aforementioned halogenated boron-containingprecursor and higher order boranes and/or carboranes, optionally in thepresence of a fluorine source.

In addition to lowering the arc voltage needed to dissociate thealternative boron-containing precursors, the alternative speciespreferably dissociate into byproducts that are volatile and will notplate the inside of the vacuum chamber and other components of the ionsource region. Further, the alternative boron-containing precursorspreferably have a low carbon content (i.e., less than 3 carbon atoms permolecule, preferably less than 2, and most preferably less than 1) ascarbon deposits tend to shorten the life of the ion source components.

An advantage of using fluorinated boron-containing precursors includesthe generation of fluorine radicals created in the ion source, saidradicals reacting with boron deposited on the walls of the ion sourceregion components, thereby keeping said components clean. Towards thatend, fluorine-containing species, e.g., F₂, may be introduced to the ionsource region during ionization to assist with component and chambercleaning processes when the fluorinated boron-containing dopant speciesdo not generate enough fluorine radicals during ionization. The amountof fluorine-containing species relative to fluorinated boron-containingdopant species is readily determined by one skilled in the art.Accordingly, one embodiment of the invention relates to a method ofimplanting boron-containing ions using a boron-containing precursorcomprising a boron-containing dopant species selected from the groupconsisting of BF₃, BCl₃, BBr₃, B₂F₄, B₂Cl₂, B(BF₂)₃CO, BF₂CH₃, BF₂CF₃,BF₂Cl, BFCl₂, BF(CH₃)₂, NOBF₄, NH₄BF₄, H₂BF₇, H₂B₂F₆, H₄B₄F₁₀, H₂BFO₂,H₂B₂F₂O₃, H₂B₂F₂O₆, H₂B₂F₄O₂, H₃BF₂O₂, H₄BF₃O₂, H₄BF₃O₃, B₈F₁₂, B₁₀F₁₂,(F₂B)₃BCO, CB₅H₉, C₂B₄H₈, C₃B₃H₇, C₄B₂H₆, C₂B₃H₇, C₂B₃H₇, CB₅H₉, C₂B₄H₈,C₃B₃H₇, C₄B₂H₆, C₂B₇H₁₃, C₂B₃H₅, C₂B₄H₆, C₂B₅H₇, CB₅H₇, C₂B₆H₈, C₂B₇H₉,C₂B₈H₁₀, C₂B₉H₁₁, C₂B₁₀H₁₂, (Cl₂B)₃BCO, and combinations thereof, and afluorine-containing species (e.g., F₂).

In another embodiment of the invention, noble gases such as neon, argon,krypton or xenon may be co-blended with the boron-containing dopantspecies, or alternatively separately fed to the vacuum chamber formixing with the boron-containing dopant species therein, thereby forminga vapor phase reagent composition. Although not wishing to be bound bytheory, it is thought that the noble gases will collide with theboron-containing dopant species and assist with the disassociation ofthe dopant species at lower arc voltages. In addition, the co-blendingof the boron-containing precursor with the noble gases makes theoperating conditions more benign. Accordingly, another aspect of theinvention relates to a method of implanting boron-containing ions usingany boron-containing precursor (e.g., BF₃ or the precursors set forthabove) and adding noble gases to increase the ionization efficiency.Preferably, for this aspect of the invention, the boron containingprecursor is BF₃.

It is also contemplated herein that the feedstock includes borontrifluoride, in addition to the alternative boron-containing precursorsdisclosed herein. For example, the feedstock may include about 0.01 toabout 90 percent by weight BF₃, based on the total weight of thefeedstock.

In practice, liquid and/or solid boron-containing precursor feedstock isvaporized using vaporization methods well known in the art, e.g.,reduced pressure, heating, etc., before or at the vacuum chamber, whilegaseous precursor feedstock is introduced directly to the vacuumchamber. An ion source generates ions by introducing electrons into thevacuum chamber filled with gaseous dopant species. Several types of ionsources are commonly used in commercial ion implantation systems,including the Freeman and Bernas types using thermoelectrodes andpowered by an electric arc, a microwave type using a magnetron,indirectly heated cathode sources, and RF plasma sources, all of whichtypically operate in a vacuum. Collisions of the electrons with thegaseous dopant species results in the creation of an ionized plasmaconsisting of positive and negative dopant ions. An extraction electrodewith a negative or positive bias will respectively allow the positive ornegative ions to pass through the aperture and out of the ion source asa collimated ion beam, which is accelerated towards the microelectronicdevice workpiece.

Cluster boron implantation allows an increase ion implant efficiency,relative to use of traditional boron precursors such as borontrifluoride, boron trifluoride, diborane, and the like. Implanters usedin the process can work at lower energies than traditional dopantdelivery processes utilizing such boron precursors. Use of clustertechnology allows for delivery of multiple borons at one time. Thepresent invention provides, in various aspects thereof, a method offorming boron hydride precursors, a source of boron hydride precursorsand a method for delivering the boron hydride precursors for boroncluster implantation.

The boron hydride diborane(6) is a gas that is toxic, flammable,pyrophoric, dangerous and has a repulsive odor. It is known to decomposeat room temperature, forming higher order boranes, such as BH₃, B₃H₇,B₄H₈, and the like. Decomposition reactions may include the following:B₂H₆→2BH₃;BH₃+B₂H₆→B₃H₉;B₃H₉→B₃H₇+H₂;B₃H₇+B₂H₆→B₄H₁₀+BH₃;B₄H₁₀⇄B₄H₈+H₂; andB₄H₁₀⇄B₃H₇+BH₃.

Because of its high rate of decomposition, the gas is generallycommercially available only at concentrations of 30% or less. Thepresent invention utilizes this natural decomposition process and theformation of higher order boranes to generate boron hydride precursorsfor use in cluster boron implantation. Preferably the formation of boronhydride precursors is performed in proximity to or at the point of useof the precursors.

In one embodiment the invention provides a pressure-controlled orflow-controlled borane source, from which the borane source material isintroduced as a gas to a reactor for reaction therein to form higherorder boron clusters, which then are flowed to a tool for boron clusterimplantation, as shown in FIG. 1.

FIG. 1 is a schematic representation of a cluster boron delivery processsystem 10 according to one embodiment of the invention. The boronprecursor is contained in a cylindrical vessel 12 having a valve headassembly 14 secured to the upper portion of the vessel. The vessel andhead valve assembly are contained in a gas box 16, in which the headvalve assembly is coupled with transfer line 18. The transfer line 18exteriorly of the gas box 16 contains a mass or pressure controller 20therein to modulate the flow of the boron precursor vapor.

The cylindrical vessel 12 preferably contains the boron source materialin a gaseous state.

Alternatively, although less preferred, the vessel may contain the boronsource material in a solid state, with the vessel being heated in thegas box, to effect volatilization of the solid to form the precursorvapor. The vessel can be heated in any suitable manner (heatingcomponents and/or devices not shown in FIG. 1), e.g., by use of aheating jacket, convective heat transfer in the gas box, or in any othermanner appropriate to generate the boron precursor vapor in the desiredamount.

The transfer line 18 is coupled at its downstream end to a reactor 22 inwhich the boron precursor is submitted to process conditions effectinggeneration of higher order boron species, e.g., higher order boranes,such as BH₃, B₃H₇, B₄H₈, and the like. The reactor 22 as shown islocated adjacently to the semiconductor tool 24, with the reactor influid supply relationship with the tool, so that the higher orderboranes flow directly into the tool from the reactor.

In various aspects of the invention, the reactor may be located separatefrom, adjacent to or within the tool. The tool can comprise for examplean ion implanter unit, or other boron precursor fluid-utilizing tool. Ina preferred embodiment, the tool is a microelectronic devicemanufacturing tool.

In preferred practice, the borane source is a gas. Such aboron-containing gas will be easy to transport. The source material, theboron-containing gas, can be stored prior to use in any manner known tothose in the art. Such storage methods can include, but are not limitedto, neat gas storage, and storage of the gas in a diluted form, in inertgases such as hydrogen, argon, helium or nitrogen. Exemplary boranesource gases include, but are not limited to diborane and pentaborane.

As the borane-containing gas is transferred from the supply vessel tothe reactor, it preferably is passed through a controller, such as themass or pressure controller 20 illustratively shown in FIG. 1. Such acontroller may regulate mass or pressure, such that the gas remains inits desired state for delivery to the reactor. Such control is anadvantage over previous methods which utilized solid material and flowthrough heat traced lines. Use of a controller is not required in theinvention, but is highly advantageous in providing a desired flow ofprecursor gas to the reactor.

In addition to the borane-containing gas, an additional reactant orreactants may be supplied. Such additional reactants may be added at anypoint in the transfer from the gas source to the reactor, or may beadded to the reactor itself. Such a reactant or reactants can forexample be utilized to improve the kinetics or efficiency of thereaction or to form more complex higher order boron species. Use of suchreactants can allow optimization of hydrogen to boron ratios to formdesired products. For example, formation of non-volatile boron polymerscan be inhibited by using a proper H₂ mixture that maximizes the yieldof non-clogging materials.

Where diborane is the gas utilized in the present invention, theconcentration of the diborane gas may range from 1000 ppm to 30% byweight. Original concentrations of a diborane gas greater than 30% arenot stable in the storage container and will decompose. When aconcentration of grater than 30% is desired to be provided to thereactor, a concentrator may be utilized in the line transferring the gasto the reactor.

Such a concentrator is schematically illustrated in the precursordelivery system shown in FIG. 2, in which a dilute diborane feed streamin feed line 30 is flowed to the H₂ Getter/Diborane Concentrator 32,with the resulting concentrated diborane being flowed to the reactor 34for generation therein of higher order boranes, as discharged from thereactor in discharge line 36.

In a situation where greater than 30% diborane is desired, theconcentrator is utilized to reduce the amount of H₂ in the line. Suchreduction of hydrogen can be achieved utilizing H₂ getters or permeationmethods, e.g., with a hydrogen permselective membrane being employed forhydrogen removal from the higher order borane species.

The reactor utilized in the practice of the invention for generatinghigher order boranes can be located near the point of use of theresulting clusters. Such a location may be separate from, adjacent to orwithin the tool for use of the clusters. Within the reactor, a reactionis induced that results in the production of boron molecules withgreater than 2 borons present. The temperature of the reaction withinthe reactor in various embodiments can be within a range of roomtemperature to 400 C, and pressure within the reactor in variousembodiments can be within a range of vacuum to 1000 psi.

For such purpose, various types of reactors can be utilized, within theskill of the art, based on the disclosure herein. Use of any reactorthat induces production of boron clusters is encompassed within thescope of the invention. Reactors that may usefully be employed in thepractice of the invention include, without limitation, heated reactors,catalytic reactors, heated catalytic reactors, UV lamps, reactors withelectric, microwave or radio frequency discharge or plasma, packedreactors, multiple stage heated reactors, hot plates, high pressurereactors and concentric tubular reactors. The types of reactors listedare not mutually exclusive, for example, a heated, packed, catalyticreactor (see FIG. 4) or a multiple stage heated, concentric reactor (seeFIG. 5) can be used in specific embodiments of the invention.

A heated reactor usefully employed in the practice of the invention caninclude any reactor that is heated. Such reactor can be a heated wallreactor, a heated packed reactor, a cold wall reactor, a reactor with aninternally heated section and a reactor containing multiple stagetemperature grading throughout the reactor volume. A heated reactorincludes any reactor where heat is utilized in induction of thereaction. Heated reactors of various types are illustratively shown inFIGS. 3-8.

A catalytic reactor usefully employed in the practice of the inventioncan include any reactor that accelerates the reaction within thereactor. Catalysts may be added to the reaction or may be in integratedpart of the reactor itself. Catalysts may include, but are not limitedto, metals such as iron, aluminum, copper, alumina, platinum, boron,carbon, carbon adsorbent and activated carbon. Where catalysts are apart of the reactor, they may be mounted to structural surfaces of thereactor, packed into the reactor as beads or pellets or the reactor mayinclude a catalyst impregnated media with any known flow design, such asa tube, honeycomb or beading. Catalyst reactors of widely varied typesmay be employed.

A high pressure reactor for use in a method or system of the inventionmay include any reactor that allows the reaction to occur at highpressure. The high pressure may be generated by any method known tothose in the art. For example, pressure within the reactor can begenerated by the use of an orifice or slit at the exit region of thereactor, such that pressure is built up in the reactor for delivery ofthe boron-containing clusters to the semiconductor tool. Typically, whenthe tool is an ion implanter, the pressure within the tool will be avacuum, e.g., subatmospheric pressure.

FIG. 3 is a schematic representation of a high pressure reactor 40, inwhich the high pressure is created by a constriction in the exit path44, such that the boron cluster formation reaction within the reactoroccurs at a higher pressure than the pressure within the tool. Thereactor has an inlet 42 in which diborane or borane mixtures can beintroduced to the reactor interior volume, and reacted therein to formlarger boron clusters that are discharged from the reactor outlet. Inthis reactor scheme, P1 and T1 are greater than P2 and T2.

A packed reactor for use in a method or system of the invention mayinclude any reactor that contains packing material. The packing materialcan be used simply to increase the surface reaction for the reaction tooccur, to improve the heat transfer, or to provide catalytic effect. Thepacking material may also include a catalyst impregnated media with anyknown flow design, such as a tube, honeycomb or beading.

FIG. 4 is a schematic representation of a heated packed reactor 50 suchas may be usefully employed in the practice of the invention. Thereactor has an inlet 60 by which diborane or borane mixtures can beintroduced into the reactor interior volume. The interior volume 52contains a surface area reaction enhancement or is packed with catalyst,and produces larger boron clusters that are discharged from the reactorin discharge line 56.

A concentric tubular reactor for use in the invention can include anyreactor that has multiple tubes. An illustrative example is shown inFIG. 5, in which multiple gases are combined for the reaction within thereactor, with the reaction occurring at a critical point in the heatedzone.

The reactor 70 of FIG. 5 includes an interior concentric tube 72 that iscoaxial with the main casing of the reactor and defines an annularpassage therebetween. The annular passage communicates in fluid flowrelationship with a reactant(s) feed inlet 74 in which reactant(s) enterin the direction indicated by arrow B. Such introduced reactant(s) atthe outlet end of the interior concentric tube 72 mix with the diboraneor borane mixtures flowed into the tube 72 in the direction indicated byarrow A. Thermal or plasma energy is introduced to the respective fluidstreams that mix in the reaction zone 76 and yield larger boron clustersthat are discharged from the reactor 70 at the outlet thereof, beingdischarged in the direction indicated by arrow C.

A multiple stage heated reactor useful in the practice of the inventioncan include any reactor that has variation in temperature from one partof the reactor to another. Such reactors may include, but are notlimited to, cold/hot reactors, and heated reactors with temperaturegrading. Such uses of temperature variations may be to maximize theefficiency of cluster conversion rates, or to control the reaction inany desirable manner. For example, the reactor can have a heated zonethat is located away from the exit of the reactor, thereby minimizingclogging that might otherwise occur.

FIG. 6 is a schematic representation of a cold/hot reactor 80 adaptedfor use in a system of the invention. The reactor 80 includes an inlet82 through which the diborane or borane mixtures are introduced to theinterior volume 83 of the reactor. The interior volume 83 has a heatedzone 84 therein, which may optionally contain a catalyst. The largerboron clusters produced in the reactor 80 are discharged from thereactor at outlet 86.

FIG. 7 is a schematic representation of a multiple stage heated reactor90 for use in a system of the invention. The reactor 90 includes aninlet for introduction of diborane or borane mixtures, schematicallyrepresented by arrow A. The reactor features multiple stage temperaturegrading, to conduct reaction that produces the larger boron clustersthat are discharged from the reactor in the outlet schematicallyindicated by arrow B.

FIG. 8 is a schematic representation of a reactor 94 that utilizesplasma or electrical, microwave or radio frequency discharge and isadapted for use in a system of the invention. The reactor 94 encloses aninterior volume 97 into which extends a tubular inlet passage 95 havingan electrical or plasma discharge region 96 for inducing reactionproducing the larger boron clusters that are discharged from the reactoroutlet 98.

A hot plate may also be used as a reactor in the practice of theinvention. On such a reactor, the diborane or other source gas is flashreacted by a surface induced reaction.

Once formed, the boron clusters can be delivered to a tool for use incluster boron implantation. Delivery from the reactor to the tool can beeffected in any suitable manner. Where the reactor is adjacent to orwithin the tool, delivery may be effected simply by the cluster boronstream exiting the reactor and passing into the tool.

The invention therefore contemplates a method of forming a boron hydrideprecursor for cluster boron implantation, comprising providing aboron-containing gas to a reactor and inducing conversion of theboron-containing gas to higher order boron-containing clusters withinthe reactor.

The boron-containing gas that is subjected to reaction for formation ofhigher order boron species can be selected from diborane, pentaborane,and any other suitable boron source reagents, including mixtures of twoor more of such source reagent species.

In various embodiments of the invention, the reactor is selected fromamong heated reactors, catalytic reactors, heated catalytic reactors, UVlamps, reactors containing an electric, microwave or radio frequencydischarge or plasma, packed reactors, multiple stage heated reactors,hot plates, high pressure reactors, and concentric tubular reactors. Thereactor can further comprise a catalyst, e.g., iron, aluminum, copper,alumina, platinum, boron, carbon, and activated carbon. The induction ofhigher order boron-containing clusters can comprise heating theboron-containing gas within the reactor, providing thermal of plasmaenergy to the boron-containing gas within the reactor, providingmultiple stage temperature grading to the boron-containing gas withinthe reactor, performing the reaction for induction of higher orderboron-containing clusters at a temperature in a range of from roomtemperature to 400° C., and/or pressure in a range of vacuum to 1000psi. The reaction can be carried out with addition of furtherreactant(s) to the reactor prior to or concurrent with the formation ofhigher order boron-containing clusters.

In one aspect, the invention contemplates a method of supplying a boronhydride precursor for cluster boron implantation, involving providing aboron-containing gas to a reactor, inducing conversion of theboron-containing gas to higher order boron-containing clusters withinthe reactor and supplying the higher order boron-containing clusters toa tool for cluster boron implantation.

In another aspect, the invention provides a boron hydride precursorsource including a boron-containing gas source, a reactor, and atransfer line or other flow circuitry interconnecting theboron-containing gas source and the reactor, optionally containing amass or pressure controller therein.

It will be recognized that a wide variety of specific arrangements maybe employed for formation of the higher order boron species for deliveryto a utilization facility for such species. The utilization facility canbe of any suitable type, e.g., including microelectronic devicemanufacturing tools such as ion implanters, deposition chambers, etc.

Thus, while the invention has been described herein with reference tovarious specific embodiments, it will be appreciated that the inventionis not thus limited, and extends to and encompasses various othermodifications and embodiments, as will be appreciated by thoseordinarily skilled in the art. Accordingly, the invention is intended tobe broadly construed and interpreted, in accordance with the ensuingclaims.

1. A method of implanting boron-containing ions, comprising: ionizing a gas-phase boron-containing compound using an ionization apparatus to generate an ion beam of boron-containing ions; and accelerating the boron-containing ions by electric field to implant boron-containing ions into a substrate, wherein the boron-containing compound comprises B₂F₄.
 2. The method of claim 1, further comprising annealing the substrate subsequent to implanting the boron-containing-ions into the substrate.
 3. The method of claim 1, wherein said ionizing is carried out in a vacuum chamber.
 4. The method of claim 1, wherein at least 15% of the boron-containing compound is ionized in said ionizing.
 5. The method of claim 4, wherein said ionizing is carried out at arc voltage of less than 100 volts.
 6. The method of claim 4, wherein said ionizing is carried out at arc voltage of less than 90 volts.
 7. The method of claim 4, wherein said ionizing is carried out at arc voltage of less than 80 volts.
 8. The method of claim 4, wherein said ionizing is carried out at arc voltage of less than 70 volts.
 9. The method of claim 1, wherein said boron-containing compound is mixed with a noble gas for the ionizing
 10. The method of claim 9, wherein said noble gas is selected from the group consisting of neon and argon.
 11. The method of claim 9, wherein said noble gas is selected from the group consisting of krypton and xenon.
 12. The method of claim 1, wherein said boron-containing compound further comprises BF₃.
 13. The method of claim 1, wherein said substrate comprises an article selected from the group consisting of semiconductor substrates, substrates for flat panel displays, and substrates for microelectromechanical systems (MEMS).
 14. The method of claim 1, wherein said ionizing is carried out using an ion source.
 15. The method of claim 14, wherein said ion source comprises an ion source selected from the group consisting of ion sources of types using thermoelectrodes and powered by an electric arc, microwave types of ion sources using a magnetron, indirectly heated cathode sources, and RF plasma sources.
 16. The method of claim 1, wherein said boron-containing compound is contained in a vessel in a gas box joined by a transfer line to a semiconductor tool in which the boron-containing ions are implanted into the substrate.
 17. The method of claim 16, wherein the transfer line contains a mass or pressure controller therein to modulate flow of the boron-containing compound to the semiconductor tool.
 18. A method of implanting boron-containing ions, comprising: ionizing B₂F₄ using an ionization apparatus including an extraction electrode to produce a collimated ion beam of boron-containing ions; and accelerating the boron-containing ions by electric field to implant boron-containing ions into a substrate. 